Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$26.33	9.424%	$28.8113	$28.81	$28.80	$28.80
Purchase #2	$74.25	9.565%	$81.352	$81.35	$81.35	$81.40
Purchase #3	$76.84	10.757%	$85.1057	$85.11	$85.10	$85.10
Purchase #4	$179.53	9.602%	$196.7685	$196.77	$196.75	$196.80
Purchase #5	$33.26	11.278%	$37.0111	$37.01	$37.00	$37.00
Purchase #6	$40.80	7.644%	$43.9188	$43.92	$43.90	$43.90
Purchase #7	$207.39	3.307%	$214.2484	$214.25	$214.25	$214.20
7 purchase totals =	$638.40		$687.2158	$687.22	$687.15	$687.20